By way of example, FIG. 1 of WO2006135984 describes a process for the reduction of metal oxides to form metalized material by contact with hot reducing gas, which is at least partially produced by catalytic reformation of natural gas wherein the heat for the endothermal reformation processes which take place during the reformation is provided at least partially by the combustion of a fuel gas. Owing to statutory regulations, it is desirable for it to be possible to efficiently separate CO2 from the off-gases produced during the process, before they are released into the environment. In the case of a process as shown in WO2006135984, the fuel gas for the reformer is combusted with air as the oxygen source, for which reason the combustion off-gas contains a large quantity of nitrogen. Correspondingly, downstream plants for removing CO2 from the combustion off-gas have to have a correspondingly large design. Additionally, only chemical absorption processes which have a large design and a high energy consumption are suitable for removing CO2 from the combustion off-gas which is at low pressure.
Furthermore, if conventional burners are used high NOx contents are present in the combustion off-gas owing to the nitrogen. Owing to ever more stringent environmental regulations, downstream deNOxing systems, in particular the process for the selective catalytic reduction of nitrogen oxides (SCR), are thus almost always required. Although high NOx contents in the combustion off-gas are prevented, on the other hand, when low-NOx burners are used, the flame pattern of such burners is disadvantageous for use in the reformer.
A further disadvantage of the use of air as the oxygen source arises from the fact that heat is transferred in the reformer, and possibly in recuperators present in the combustion off-gas lines, only to a relatively small extent by radiation and predominantly by convection owing to the high nitrogen content, convection bringing about a much less efficient transfer of heat than radiation.